[doxygen][mineralization] add missing opening parentheses in solid storage term in all min-models

See merge request !2214

[common][partial] Add MTBV containing const references

See merge request !2215

[math] Add linear table interpolation with two arguments

See merge request !2216

[readme] Add website's getting started guide to doc ressources

See merge request !2213

Fix macro calls and changelog entry

See merge request !2211

Replace calls to deprecated `DUNE_VERSION_NEWER_REV(DUNE_ISTL,2,7,1)`
by `DUNE_VERSION_GT_REV(DUNE_ISTL,2,7,0)` which also reads better than
the `GTE` version, as Dune 2.7.1 hasn't been released yet. Fix the
call to `DUNE_VERSION_GT(DUNE_ISTL,2,7)` in the solver factory
backend which would break things in case of a 2.7.1 release. Adapt
the corresponding changelog entry.

[changelog] Add comment on ISTL solverfactory

See merge request !2209

Feature/improve extract line data

See merge request !2207

* Make make dir of output dir more consise and handle "  " case
* simplify verbose output

Feature/staggered assembler fix forwarding implicit flag

See merge request !2206

When multiple vtk files were given as arguments to the script together
with a base name for the output .csv files, a single csv file was
created that contained the data of the last given vtk file. This commit
adds an index to the file names in case multiple vtk files are provided.

[rans][fluxvars] adapt coefficient averaging with boundary check

See merge request !2204

Feature/cc internaldirichlet

Closes #772

See merge request !2202

* rename and deprecated function updateBoundary -> updateDirichletConstraints

New concept for extrusion of grid geometries

See merge request !2188